Caption: Using a manganese bath. Automated arm holding a neutron source container (small sphere) above two manganese baths (large spheres). Neutrons are normally stable particles found in the centre of an atom. However, they are emitted by certain radioactive materials, such as the isotope californium-252 (Cf-252). The manganese bath measures neutron emission rate, the number of neutrons emitted per second by radioactive neutron sources. Photographed at the National Physical Laboratory, in Teddington, UK.